Step 1 Simmer the lemon juice and sugar in a saucepan over medium-high heat to dissolve the sugar. Cool well, about 1 hour, then stir in the lemon oil and citric acid.
Step 2 Prepare each glass with some ice cubes, then pour about 2 to 4 tablespoons of the lemon mixture into each glass. Fill them with chilled Perrier or spring water.